The present invention relates generally to prostheses for implantation within body lumens, and more particularly to coiled-sheet stents that include selectively thinned regions, and to methods for making such stents.
Tubular prostheses or xe2x80x9cstentsxe2x80x9d are often implanted within blood vessels, for example, within the coronary and carotid arteries, for treating atherosclerotic disease that may involve one or more stenoses. Stents generally have a tubular shape capable of assuming a radially contracted condition to facilitate introduction into a patient""s vasculature, and an enlarged condition for engaging the vessel wall at a treatment location. In its contracted condition, the stent may be placed on or in a delivery device, such as a catheter, percutaneously introduced into a patient""s vasculature and advanced to a target treatment location, such as a stenosis, occlusion, or other lesion within a blood vessel. Once at the treatment location, the stent may be deployed and expanded to its enlarged condition, thereby engaging the wall of the vessel and substantially anchoring the stent in place.
Plastically deformable tubular stents have been suggested that are initially provided in their contracted condition, and placed over a balloon on a delivery catheter. At the treatment location, the balloon is inflated to plastically deform the stent until it is expanded to its enlarged condition. Thus, the stent may be expanded to any size within a specified range to ensure that the stent substantially engages the wall of the vessel.
Self-expanding tubular stents have also been suggested that are biased to assume their enlarged condition but may be radially compressed to a contracted condition. The stent may be mounted to a delivery device and constrained in a contracted condition during delivery, for example, by an overlying sheath. At the treatment location, the stent may be released, for example, by retracting the overlying sheath, the stent automatically expanding to its enlarged condition to engage the vessel wall.
In addition to tubular stents, coiled-sheet stents have been suggested. A flat sheet is rolled into a spiral shape having overlapping inner and outer longitudinal sections that defines a contracted condition. The coiled-up sheet may be biased to at least partially unroll to assume an enlarged condition, and/or may be unrolled and radially expanded using a balloon. The coiled-sheet stent may have a lattice-like structure and a plurality of fingers or teeth along the inner longitudinal section for engaging openings in the lattice. Once the coiled-sheet stent is expanded at a treatment location, the fingers on the inner longitudinal section may engage corresponding openings in the lattice to lock the stent in the enlarged condition.
Coiled-sheet stents may provide enhanced anchoring within the blood vessel because the size of the fully expanded stent may be more precisely controlled. A conventional rectangular lattice, such as that disclosed in U.S. Pat. No. 5,443,500 issued to Sigwart, however, may result in a coiled-sheet stent that is more rigid transverse to its longitudinal axis than desired, i.e., that may not bend as easily as desired, particularly when being delivered through tortuous anatomy.
Accordingly, it is believed that a stent that provides enhanced flexibility would be considered useful.
The present invention is directed to prostheses for implantation within body lumens, and more particularly to stents that include selectively thinned regions to enhance the flexibility of the stent, and to methods for making such stents.
In accordance with one aspect of the present invention, a stent is provided that includes a generally tubular body having a longitudinal axis and a circumference, and having a size configured for introduction into a body lumen. A plurality of cylindrical bands are formed in the tubular body, each band including a generally zig-zag pattern. The generally zig-zag pattern may include a series of sequential diagonal elements connected to one another and extending about the circumference, the diagonal elements preferably having a generally arcuate shape. All diagonal elements in each band are preferably oriented in either a clockwise or counter-clockwise direction about the circumference to facilitate packing of the stent.
A plurality of longitudinal connectors are provided extending between and connecting adjacent cylindrical bands, the longitudinal connectors having reduced thickness regions having a thickness t1 in a radial direction that is substantially smaller than a thickness t0 of the adjacent cylindrical bands. In a preferred form, the thickness t1 of the reduced thickness regions is not more than about two thirds the thickness t0 of the cylindrical bands, and more preferably not more than about one half.
In a preferred embodiment, the tubular body is a coiled-sheet, although the principles of the present invention may apply equally well to substantially enclosed tubular stents. The tubular body is generally expandable between a contracted condition for facilitating introduction into a body lumen and an enlarged condition for engaging a wall of a body lumen. Preferably, the tubular body is biased towards the enlarged condition, and may exhibit temperature-activated shape memory properties. The generally zig-zag pattern may be expandable between an unstretched condition and a stretched condition, the zig-zag pattern being biased towards the stretched condition above a transition temperature, which is substantially below body temperature.
In accordance with another aspect of the present invention, a stent is provided that includes a generally tubular body having a longitudinal axis, a circumference, and a thickness t0, and having a size configured for introduction into a body lumen. A plurality of cells are formed in the tubular body, a plurality of connectors extending between and connecting adjacent cells, and a plurality of slots are formed in the tubular body and oriented substantially perpendicular to the longitudinal axis about the circumference of the tubular body, the slots defining a thickness t1 that is substantially less than the thickness t0 of the tubular body.
In accordance with still another aspect of the present invention, a method for fabricating a stent is provided that includes providing a flat sheet including a length, a width, and a thickness t0. A plurality of openings are formed in the sheet to define a multi-cellular structure. A plurality of slots are formed in the sheet, e.g., by cutting into the sheet with a saw, that are aligned substantially perpendicular to the length of the sheet, the slots having a reduced thickness t1 that is less than the thickness t0 of the sheet. Preferably, the sheet is formed from a shape memory alloy, and the plurality of slots are formed in the sheet without substantially changing mechanical properties of the shape memory alloy. The sheet is rolled about its length into a tubular body, the tubular body having a diameter configured for introduction into a body lumen.
In a preferred method, the step of forming a plurality of openings in the sheet includes forming a plurality of cells and longitudinal connectors in the sheet. Longitudinally adjacent cells are preferably connected to one another by the longitudinal connectors, which are aligned in sets substantially perpendicular to the length of the sheet. The plurality of slots are preferably formed such that a slot intersects each set of longitudinal connectors, thereby providing a reduced thickness region in each of the longitudinal connectors. The reduced thickness regions of the connectors may enhance a flexibility characteristic of the resulting stent, e.g., facilitating bending of the stent when it is advanced through tortuous anatomy.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.